(1) Conventionally, a magnetic sensor is pressed against a piston rod by a spring or it is fixed to a holder or a cover by a pin (e.g. refer to a gazette of Japanese Utility Model Publication No. 63-97806).
In such an arrangement, the magnetic sensor is insufficiently regulated in the rotary direction thereof owing to a play of bolt holes or pin holes of the cover whereby an output and accuracy of the sensor are not improved.
Furthermore, the holder and the cover are likely to fall off by the force of the spring and the assembling thereof was difficult.
Still furthermore, there are such problems in that the position between the magnetic sensor and a spring rod, which causes the deterioration of, the output and accuracy of the sensor, should be regulated sufficiently for the rotary angle of the magnetic sensor so as to stabilize the output and accuracy of the sensor and when a housing and the cover are assembled with the head, the force of the spring acts in the direction to remove the housing and the cover from the head so that the assembling of the housing and the cover aligning with the pin hole is difficult and many steps are required for such an assembling.
(2) In the device of this type, the sensor and the housing are positioned by the pin and the housing and the block are further positioned by another pin. Since the positioning and the mounting angle of the sensor generally affect the output of the signal seriously, the positioning should be performed by way of many pins in the arrangement as set forth above, which causes each measurement error to be accumulated to thereby bring about a large dispersion in the output of the sensor.
(3) Still furthermore, in the device of this type, a block provided with a sensor is mounted on a cylinder head and is adjusted so that the cylinder head is subjected to a tap process aligning with the bolt holes of a block in the site.
There are such other means as disclosed in Japanese Utility Model Laid-Open Publication No. 1-178207 which discloses a fixing means for fixing a sensor by a two-splitted spacer or as disclosed in Japanese Utility Model Laid-Open Publication No. 64-29516 in which a sensor for detecting the movement of a piston rod is mounted on a cylinder head at the portion adjacent to a joint sensor which incorporates a sensor amplifier thereinto for processing an output signal of the sensor.
Such mounting devices have such a drawback in that since the cylinder and the sensor are subjected to the process after they are assembled, the process is difficult and cost high.
In Japanese Utility Model Laid-Open Publication No. 64-29516, since the sensor is mounted on the cylinder head, if the cylinder head is of a screwing type, it is difficult to set the sensor relative to a magnetic scale on the piston rod at a desired position.
Furthermore, since the cylinder head specially serves for mounting the sensor thereon, elements other than the sensor should be replaced and repaired even if the cylinder head is troubled other than the sensor, which causes the problem in maintainability thereof.
It is an object of the present invention to solve the drawbacks or problems as set forth in items (1), (2) and (3).